1. Field of the Invention
Embodiments of the present invention generally relate to a processing apparatus for planarizing or polishing a substrate. More particularly, the invention relates to polishing pad design for planarizing or polishing a semiconductor wafer by electrochemical mechanical planarization.
2. Description of the Related Art
In the fabrication of integrated circuits and other electronic devices on substrates, multiple layers of conductive, semiconductive, and dielectric materials are deposited on or removed from a feature side, i.e., a deposit receiving surface, of a substrate. As layers of materials are sequentially deposited and removed, the feature side of the substrate may become non-planar and require planarization. Planarization is a procedure where previously deposited material is removed from the feature side of a substrate to form a generally even, planar or level surface. The process is useful in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage and scratches. The planarization process is also useful in forming features on a substrate by removing excess deposited material used to fill the features and to provide an even or level surface for subsequent deposition and processing.
Chemical mechanical polishing (CMP) and Electrochemical Mechanical Planarization (ECMP) are two exemplary processes used to remove materials from the feature side of a substrate. In one exemplary CMP process, a web-type CMP pad containing abrasive particles is adapted to contact the feature side of the substrate using physical abrasion to remove materials. The CMP pad is attached to an apparatus having a rotating platen assembly. The apparatus also has a substrate carrier, such as a polishing head, that is mounted on a carrier assembly above the pad that holds a substrate. The polishing head places the substrate in contact with the pad and is adapted to provide downward pressure, controllably urging the substrate against the pad. The pad is moved relative to the substrate by an external driving force and the polishing head typically moves relative to the moving pad. Typically, the CMP pad includes a plurality of raised portions surrounded by a plurality of depressions. The raised portions of the CMP pad are distributed in a uniform pattern which provides uniform contact to the feature side of the substrate during operation.
The ECMP process typically uses a pad having conductive properties adapted to combine physical abrasion with electrochemical activity that enhances the removal of materials from the feature side of the substrate. The pad is attached to an apparatus having a rotating platen assembly that is adapted to couple the pad to a power source. The apparatus also has a polishing head that is mounted on a carrier assembly above the pad that holds the substrate. The polishing head places the substrate in contact with the pad and is adapted to provide downward pressure, controllably urging the substrate against the pad. The pad is moved relative to the substrate by an external driving force and the polishing head typically moves relative to the moving pad. A chemical composition, such as an electrolyte, is typically provided to the surface of the pad which enhances electrochemical activity between the pad and the substrate. The ECMP apparatus effects abrasive or polishing activity from frictional movement while the electrolyte combined with the conductive properties of the pad selectively removes material from the feature side of the substrate.
Although ECMP has produced good results in recent years, there is an ongoing effort to develop pads with improved polishing qualities combined with optimal electrical properties that will not degrade over time and require less conditioning, thus providing extended periods of use with less downtime for replacement. Inherent in this challenge is the difficulty in producing a pad that will not react with process chemistry, which may cause degradation, or require excessive conditioning.
Typical pads used in this process have an upper surface to contact the feature side of the substrate that is substantially flat. Variations may include slightly raised projections that extend from the pad's upper surface. This upper surface may not sufficiently contact the feature side of the substrate, possibly leaving regions of the feature side without sufficient or stable electrical bias. This regional or intermittent bias may adversely affect the polishing process.
Therefore, there is a need for a planarizing or polishing pad with an upper surface that combines the uniform contact of a CMP pad with the conductive properties of an ECMP pad in order to provide abrasion while communicating a stable electrical bias to the feature side of the substrate.